This invention pertains to measuring and detecting coagulation and coagulation-related factors in fluids, such as human blood. More specifically, this invention pertains to improvements in cartridges of the type wherein gas flows through a fluid sample in a reaction chamber of the cartridge to create bubbles of fluid for the purpose of detecting and analyzing coagulation, coagulation time, and other and coagulation-related factors.
Examples of gas flow cartridges and gas flow techniques for detecting and analyzing coagulation and coagulation-related factors are disclosed in the aforementioned application and in U.S. Pat. Nos. 4,000,972 and 4,074,971, all assigned to the assignee of the present invention. In general, these gas flow cartridges are characterized by a vertically oriented enclosure or tube-like member which has a reaction chamber located therein above a reagent chamber. The reagent chamber contains various additives or reagents which are mixed with the fluid to be tested in the reaction chamber. The reagent chamber is loaded with reagent at the time when the cartridge is manufactured. The reaction chamber is loaded with the fluid sample to be tested at the time of the test. An actuator mechanism operable in conjunction with the cartridge collapses the reagent chamber and forces its contents into the reaction chamber. Gas is injected into the reaction chamber and flows upward through its contents. Bubbles of fluid are formed and coagulation is detected by detecting coagulation of the fluid which forms the bubbles.
In the aforesaid application Ser. No. 434,718, the gas flow cartridge employs resilient sealing plug members positioned at the upper and lower ends of the reagent chamber. These resilient members each include a dome portion having slits formed therethrough. The resiliency of the material normally holds the slit in a closed position to seal the liquid reagent within the reagent chamber from the time of manufacture until it is ultimately used some period of time later. It has been determined, however, that to obtain the best fluid tight closure of the slit in the dome member, the slit must be formed at a relatively precise length. Variations in the length of the slit and in other construction dimensions of the dome portion and in the resiliency of the material of the dome portion can result in leaks of reagent from the reagent chamber prior to use of the cartridge. Although coating the surfaces of the dome portion at the closed slit with low shear strength sealant reduces the possibilities of leaks, the coating technqiue has not proved universally successful in terminating leaks under all conditions. A reduction in the amount of reagent in the reagent chamber due to leakage prior to the analytical test can alter the test results under some conditions.
Slits formed smaller than the optimum size or length are too restrictive to the gas flow. An excessive back-pressure develops and flow of gas through the contents of the reaction chamber is reduced. Variable effects on coagulation are created and, as a result, statistical reliability in detecting coagulation can be affected.
Slits which are larger and smaller than the critical size also have a corresponding effect on the size of bubbles created. Variations in bubble size also introduce variables which may have an effect on the consistent detection of coagulation.
The hydrostatic pressure necessary to force open the slit of the resilient dome portion can also cause reagent leaks around the nozzle which injects the gas into the reaction chamber. This pressure is caused by the resiliency of the dome portion when the slit is held open by the gas pressure flowing through the slit.
These factors, among others, underly the improvements of the present invention.